1. Field of the Invention
The present invention relates to a hollow needle for an ophthalmic surgical instrument that crushes lenses by actuating the hollow needle at high frequency, and removes lens debris by suction. The hollow needle has a suction channel and a segment radially expanding toward a ring-shaped distal end of the hollow needle. The channel consists of bores extending coaxially with the suction channel from the distal end into the hollow needle, and has stepped diameters connected by conical ring shoulders.
2. The Prior Art
It is known that cataract operations are successfully performed in the field of the ophthalmic surgery using hollow needles actuated by ultrasound. In such operation, the hollow needle, which is axially movable at high frequency, is guided directly up against the cataract. The ultrasonic waves emitted from the ring-shaped distal end of the needle lead to emulsification of the tissue. The separated lens pieces are then removed by suction through the hollow needle together with the rinsing liquid previously admitted to the eye.
In order to facilitate the removal of old cataracts, where the lens tissue is very hard, additional measures have been implemented in order to intensify or focus the ultrasonic field emitted from the needle point. A hollow needle of this type is known, for example from German Patent 43 13 245 A 1. The suction channel in this needle has a segment extending radially in the direction of the point of the needle. This segment consists of three stepped bores extending coaxially with each other from the distal end of the hollow needle into the needle, so that the cross section of the suction channel widens step by step in the direction of the aperture of the point of the needle. The ring or annular shoulders extending between the bores serve as additional surfaces for reflecting the ultrasonic waves, which results in an intensified ultrasonic field in front of the point of the needle. Additional focusing of the emitted ultrasonic waves is accomplished by providing the ring shoulders with a conical shape.
The known hollow needle has been successfully employed in the majority of cases. However, with cataracts having particularly hard lens tissue, the ultrasonic field emitted by the hollow needle may not suffice for emulsifying the lens tissue completely. Larger pieces of the lens tissue are crushed further on the annular shoulders, which may cause clogging of the suction channel.